1. Field of the Invention
The present invention relates to a signal processing device for effectively eliminating a noise from a signal containing a noise, such as a signal with a mingling of noise.
2. Description of the Related Art
FIG. 1 is a diagram showing the outline of a prior art noise suppression system (Japanese Patent Application Publication No. 63-500543).
In FIG. 1, a voice-plus-noise signal at an input is divided by a channel divider 19 into many selected channels. Then, the gain of these individual pre-processed voice channels is adjusted by a channel gain modifier 21 in response to a modified signal described later so that the gain of the channels exhibiting a low voice-to-noise ratio is reduced. Then, the individual channels comprising the post-processed voice are recombined in a channel combiner 26 to form a noise-suppressed voice signal available at an output.
Also, the individual channels comprising the pre-processed voice are applied to a channel energy estimator 20 which serves to generate energy envelope values for each channel. The post-processed voice is inputted into a channel energy estimator 22. The post-processed estimated channel energy is utilized by a background noise estimator 23 to determine voice/noise.
A channel SNR estimator 24 compares the background noise estimate of the estimator 23 to the channel energy estimate of the estimator 20 to form an SNR estimate. The SNR estimate is utilized to select a specified gain value from a channel gain table comprising experimentally beforehand determined gains. A channel gain controller 25 generates the individual channel gain values of the modified signal in response to the SNR estimate.
However, such prior art noise suppression system adjusts the gain to suppress noise without eliminating noise, so that a sufficiently noise-eliminated signal cannot be obtained.